1. Field
The present invention relates generally to registration systems and, more particularly, to registering nodes in a communication network.
2. Description of the Related Art
In conventional time division multiplex data communication systems where the exact participants are unknown, a procedure must exist to account for and handle the possibility of messages being transmitted at substantially the same time and, thus, being “garbled.” The procedures to handle the garbled messages vary depending on the communication system. In a classic ALOHA network, a network participant transmits its message and listens at the same time, or after some predefined delay. If the transmitting network participant hears its own garbled message, then the network participant backs-off and waits a predetermined amount of time before retransmitting its message.
A variation to the classic ALOHA network is the slotted ALOHA network scheme. Slotted ALOHA improves on the performance of a pure ALOHA network by requiring the network participants to transmit within predefined time boundaries. A drawback to this approach is its requirement that one participant provide a timing marker for the other network participants.
Carrier Sense Multiple Access (CSMA) networks provide an improvement over ALOHA networks by requiring that each participant listen for another transmission before attempting to transmit. In Carrier Sense Multiple Access with Collision Detection (CSMA/CD) schemes (e.g., IEEE 802.3), a sender (i.e., a transmitting participant) must determine that the voltage level on the medium is not greater than that generated by the sender, (i.e., itself). If the detected voltage level is greater, a collision is detected (e.g., another participant is also transmitting). In IEEE 802.3, the sender will then follow a binary exponential back-off scheme until it can send its message in the clear (i.e., without collision).
Multiple Access with Collision Avoidance (MACA) techniques use the broadcast of RTS and CTS messages to minimize the likelihood of collisions. However, when a collision does occur, a binary exponential back-off scheme is used to determine when a retry is to be attempted.
The aforementioned methodologies have at least two things in common. First, each participant in the network is responsible for determining if a collision has occurred. Second, retries occur at random times after the collision, either over a fixed period of time or over a period of time that continually expands, possibly exponentially. These two factors are the basis for potential drawbacks with the aforementioned schemes.
One drawback is that each unit in the network must be capable of detecting collisions, potentially even while the unit is transmitting a message. In radio-frequency-based networks, this may be a difficult, if not impossible, task. Another drawback is that, if a network is lightly loaded and the time within which units may retry transmissions after detecting a collision is fixed, there may be a significant amount of wasted time. Alternatively, if the network is heavily loaded, collisions may be excessive, and no message gets through. If the retry time is permitted to expand, then the delay time might, again, be excessive.
One possible solution to the bus contention and message collision problems is to use a command-response scheme. The command-response approach requires a primary, or “base,” unit that controls all communication between the network participants. That is, the secondary, or “remote,” units will not transmit unless commanded by the base. While this addresses the bus contention problem once the network is established, a drawback is the requirement that the base unit know the identifiers of all remote units on the network. The problem of initially registering the remote units into the network when their number and identifiers are unknown still remains. One approach would be to use the aforementioned collision resolution methodologies to initially set up the network, but, this would incur all the problems inherent in the collision resolution methodologies, if only for the initialization phase.
One of the inherent problems is potential and likelihood of collisions. Where a network contains a large number of nodes, it is very likely that a substantial number of these nodes will be simultaneously transmitting during the initialization phase and, thus, causing a collision. The voltage or energy level of a collision is proportional to the number of nodes that participated in or contributed to the collision, and a high voltage or energy level associated with a collision can have damaging consequences.
For example, in a radio frequency (RF) network with a large number of nodes capable of communicating with one another, a collision involving a large number of these nodes will result in a substantial increase of energy in the RF field. The resulting increase of energy in the RF field can have drastic consequences depending on the environment in which the RF network is operating. By way of example, an increase of energy in the RF field can cause the detonation of energy sensitive devices or materials, can have harmful side effects for humans or animals, as well as other undesirable side effects. Therefore, it may be important to limit the number of nodes (i.e., transmitters) that can transmit at any one time, thus, limiting the energy in the RF field by reducing the interference and RF noise.
Thus, a system and method for initializing a data communication network without a priori knowledge of the identity of the node addresses in the network, and which avoids the issues and problems associated with collision resolution methodologies is desired. Additionally, a system and method of limiting the number of nodes that can transmit at any one time is also desired. Furthermore, a system and method of registration that is accomplished in a deterministic amount of time is likewise desired.